The present invention relates generally to wind tunnels and more particularly to a wind tunnel adapted to simulate reasonably accurately the head-on interaction of a high power laser beam and an object moving in the atmosphere.
Wind tunnels or air flow test stands are generally used for aerodynamically simulating flight conditions, e.g., aerodynamic flow fields and shear loads on the frontal regions of test vehicles or models. In special applications of these test stands it is intended to provide, e.g., an aerodynamic sea level environment with subsonic and supersonic test stream velocities in which target models are subjected to a frontal illumination with a high energy laser beam. The laser studies are important, e.g., in determining the lethal and vulnerability effects of laser beam impingement on aerodynamic vehicles and accompanying electronics. However, it is imperative that beam distortion, thermal blooming and nonuniform flow with high turbulence are precluded in order to obtain useful experimental data.
In a conventional wind tunnel low turbulent uniform flow can be obtained through the use of a stilling or settling chamber. A settling chamber is a segment of the wind tunnel which normally consists of a large volume reservoir located immediately upstream of the testing region. Usually the desired flow characteristics are attained through an appropriate use of low turbulence screens, e.g., "egg-crate" or similar flow straighteners and settling chamber wall contouring; see for example U.S. Pat. NO. 2,805,571 to Graham and U.S. Pat. No. 3,403,277 to Way et al. The most practical and economical means of illuminating the frontal region of a test model with a laser beam appears to be to transmit the beam through the stilling chamber. An alternative is to bore an orifice or orifices in the inlet to the primary nozzle. This latter method however would be extremely expensive due to the high dimensional tolerances required. To provide a laser beam entrance opening downstream of a conventional stilling chamber would produce unacceptable air flow disturbances or would require an expensive mirror system to direct the laser beam. Finally, it should be remembered that in any provision of a laser beam entrance it is imperative to prevent beam distortion, thermal blooming and nonuniform flow with high turbulence.